Conventionally, for example, in a continuous galvanized line, excess molten zinc is blown off by jetting pressurized air or pressurized gas from an air knife unit (e.g., configured using air nozzles) against a steel plate, which passes a molten zinc tank and runs while being pulled up, to obtain a desired plating thickness. In such a case, if the steel plate vibrates in a direction in which the steel plate approaches and separates from the air knife unit, the distances between the nozzles and the steel plate fluctuate. As a result, in some cases, pressure (a jet force) received by the steel plate fluctuates and the thickness of plating becomes uneven, causing deterioration in quality.
Therefore, there has been conceived an electromagnetic vibration suppression device which controls electric currents fed to electromagnets arranged to be opposed to each other in positions across a running steel plate to thereby control an attractive force of the electromagnets and reduce the vibration of the running steel plate (e.g., Patent Literature 1). The electromagnetic vibration suppression device of this type includes a plurality of sets of displacement sensors arranged in the width direction of the steel plate, and is configured to detect a relative position (distance) to the steel plate, provided to be associated with the respective electromagnets and control electric currents fed to the respective electromagnets on the basis of the relative position (distance) to the steel plate detected by the respective displacement sensors.
Incidentally, the steel plate running between the opposed electromagnets sometimes meanders in the width direction. Since an edge position (an end edge) of the steel plate changes before and after the occurrence of the meandering, there is a demand for a control specification for adjusting output currents of the respective electromagnets according to the change in the edge position.
Therefore, Patent Literature 1 discloses an aspect includes a plurality of sensors (edge position detection sensors), which are different from the displacement sensors, arranged such that an edge position of a running steel plate can be always detected at a predetermined pitch in the width direction of the steel plate, in positions where the sensors could be opposed to the edge position of the steel plate, and is configured to determine, with the respective edge position detection sensors, whether the steel plate is present, and, when the presence of the steel plate is detected, drive electromagnets associated with the edge position detection sensors and, on the other hand, when the presence of the steel plate is not detected, stop driving of the electromagnets associated with the edge position detection sensors.